The figure above is a scenario when a link failure occurs. As shown above, when a link failure occurs between port 28 of SW1 and port 27 of SW2, ERPS will automatically function. When ERPS functions, the state of port 27 of SW1 will change from blocking to connecting and the port 27 of SW1 will become forwarding less then 50msec. The switch is under Protection mode. It applies to each switch in this network.
Use command "SW_1#show erps" to check the state of each switch:
SW_1#sh erps ERPS Status : Enabled Number of ERPS Domains : 1 Domain State MEL Enabled West East RPL Owner Ctrl VLAN ------------ ---------- --- ------- -------- -------- --------- --------- Edge-Core Protection 1 Yes Eth 1/27 Eth 1/28 Yes 1
SW_1#sh erps domain Edge-Core Domain Name : Edge-Core Admin Status : Enabled MEG Level : 1 Node ID : 70-72-CF-58-F9-0B Node State : Protection West Port : Eth 1/27 (Forwarding) East Port : Eth 1/28 (Blocking) RPL Port : West RPL Owner : Enabled Holdoff Timer : 0 ms Guard Timer : 500 ms WTR Timer : 5 minutes Control VLAN : 1 Non-ERPS Device Protect : Disabled Propagate TC : Disabled
If the link between port 28 of SW1 and port 27 of SW2 is reconnected, port 28 of SW1 and port 27 of SW2 remained in blocking state.
After WTR Timer 5 minutes, west port 27 goes back to blocking, port 28 becomes forwarding, and the status of SW1 changes back to Idle mode.
SW_1#sh erps domain Edge-Core Domain Name : Edge-Core Admin Status : Enabled MEG Level : 1 Node ID : 70-72-CF-58-F9-0B Node State : Idle West Port : Eth 1/27 (Blocking) East Port : Eth 1/28 (Forwarding) RPL Port : West RPL Owner : Enabled Holdoff Timer : 0 ms Guard Timer : 500 ms WTR Timer : 5 minutes Control VLAN : 1 Non-ERPS Device Protect : Disabled Propagate TC : Disabled